<template>
    <ul class="list" >
        <li class="item" v-for="item of letters" :key="item"
        :ref="item"
        @click="handleLetterClick"
        @touchstart="handleTouchStart"
        @touchmove="handleTouchMove"
        @touchend="handleTouchEnd">{{item}}</li>
    </ul>
</template>
<script>
export default {
    name:'CityAlphabet',
    props:{
        cities:Object
    },
    computed: {
        letters () {
            const letters = []
            for(let i in this.cities) {
                letters.push(i)
            }
            return letters
        }
    },
    data () {
        return {
            touchStatus: false,
            startY: 0,
            timer: null
        }
    },
    updated () {
        this.startY = this.$refs['A'][0].offsetTop
    },
    methods: {
        handleLetterClick (e) {
            this.$emit('change', e.target.innerText)
        },
        handleTouchStart () {
            this.touchStatus = true
        },
        handleTouchMove (e) {
            if(this.touchStatus) {
                if(this.timer) {
                    clearTimeout(this.timer)
                }
                this.timer = setTimeout(() => {
                    const touchY = e.touches[0].clientY - 79
                    const index = Math.floor((touchY - this.startY) / 20)
                    if(index >= 0 && index < this.letters.length) {
                        this.$emit('change', this.letters[index])
                    }
                },16)
            }
        },
        handleTouchEnd () {
            this.touchStatus = false
        }
    }
}
</script>
<style lang="stylus" scoped>
    @import '~styles/varibles.styl'
    .list
        display flex
        flex-direction column
        justify-content center
        position absolute
        top 1.58rem
        right 0
        bottom 0
        width .4rem
        .item
            text-align center
            line-height .4rem
            color $bgColor
</style>